Important Issues which stop to migrate Zimbra

At present we are using MS Exchange server for our entire organization. We have plan to implement Zimbra CS for our Indian employees. The zimbra server will get share address book from Exchange server and authentication information from SUN Directory server in Swden. But there is two issues which stop us implementing the project:

Issue 1.

We need to migrate employees mail account from Exchange to Zimbra CS. We can not use Migration Wizard process because we do not access the Exchange server as it is maintaing by third party. So there is any other ways to migrate the mail account from Exchange server to Zimbra Server?

Issue 2.

We will use thunderbird as mail client and lighting to schedule calender. Is it possible to synchronize calender entry in lighting with calender of Exchange Users?